The invention relates to a scanning and detection means, and particularly refers to a simultaneous multiple energy scan system.
The present invention falls in the category of X-Ray inspection equipments normally used in some fields like medical, research, security etc. The technical innovations applied to this system make the device applicable in any field, particularly when it is necessary to investigate simultaneously organic and inorganic materials and a very low radiation is required.
From U.S. Pat. No. 4,873,708 it is known to provide a digital radiographic imaging system with a homogenous screen. The light efficiency of this system is high but the energy efficiency has a peak and saturation occurs, especially if objects of different materials, such a organic and inorganic materials, shall be scanned.
Thus it is an object of the present invention to provide a scanning and detection means, which has an equalized energy efficiency in a wide band of incident radiations.
This object is settled by claim 1. Advantageous developments may be taken from the subclaims.
A rotating spot of low power wideband spectra of radiant energy (X Ray, UV or other radiation) is generated from one source, passes through an object which is to be investigated, and reaches a special screen composed of a mixture of fluorescent components capable of different fluorescent in response to different incident wavelength of radiant energies.
The light generated by this screen is selectively converted into electrical signals and digitized in order to obtain a computerized picture. The image carried out with this multiple frequency radiation and selective light conversion is more accurate than the standard images obtained with other radiation inspection systems and is capable to resolve both organic and inorganic materials in the same picture.
This feature makes it possible to investigate all materials in only one scan period (few seconds for complete human body) so there is no need to rescan the same subject at different energy levels and consequently the object or subject absorbs less radiations.
It has been proposed to provide a scanning and detection means such that it comprises one single energy radiation source and one screen capable to convert the incident energy in light. With this systems it is possible to investigate different materials in the same object, but in the same picture it is possible to resolve materials with only slightly different density, being dependent of the applied energy.
To investigate other materials with very different density it is necessary to change the incident energy and to rescan the object. In any case the types of materials in the same picture are limited by the generated energy and by the type of the used screen. An extension of this apparatus would be to provide two different screens. In this case it is possible to increase the kinds of different density materials visible in the same scan but it is necessary to elaborate and mix the two pictures generated by the two screens.
Because the radiation penetration capability increases when the frequency of the radiation increases, it is necessary to choose the frequency of the applied radiation function of the density of the subject to investigate. E.g. for an X-Ray system it is possible to work with a soft source (few KeV) or with a hard source (hundreds of KeV) and the penetration is very different. More organic or in organic materials are normally used to realize the screen to detect this X-Ray. These materials are normally grouped in phosphors (ZnS, ZnCdS, etc.), rare earth oxides (Gd2O2S:Tb, La2O2S:Eu, (Zn, Cd)S:Ag, Csl:Na, and ZnCdS), oxysalts, silicates (Zn2SiO9, Mn, Y2SiO5: Ce, etc.), etc., which have different energy efficiencies and light emission peaks at different wavelengths, e.g., 420 nm for Lu2SiO5:Ce; 440 nm for GdAlO3:Ce; 480 nm for CdWO4; 560 nm for the Csl;Tl, etc.
Considering the absorption characteristic curve, the emission wavelength and the energy efficiencies for each of this materials, it is possible to generate one mixture of this, capable of converting to light a wideband of incident radiation of interest for the particularly inspection without peak of saturation.
Because of the very large number of these materials there are infinite possible combinations and it is possible to generate a general purpose screen (e.g. working from 70 to 160 KeV) or to realize a particular screen capable to highlight one subband of incident energy with respect to another and so on. This allows to investigate practically all materials (organic and/or inorganic) because of the possibility to reduce the high different density in relatively low difference in light.
The proposed invention uses only one energy source capable to generate a low power wideband spectra of energy in order to penetrate simultaneously all different density materials and only one screen, composed of a mixture of different fluorescent materials, capable of converting the different incident spectra of energy into different levels of light (or colors). This allows to resolve in the same picture organic and inorganic materials with very high difference in density. The image reconstruction is proposed with a linear scan system, but it is also possible with an areal system.